1. Field of the Invention
The present invention relates to the catalytic hydrocyanation of ethylenically unsaturated nitriles into saturated dinitriles, and, more especially, to the catalytic hydrocyanation of pentenenitriles into adiponitrile, one of the basic starting materials for the production of polyamide or nylon 66.
2. Description of the Prior Art
French Patent No. 1,599,761 describes a process for the preparation of nitriles by addition of hydrocyanic acid to organic compounds containing at least one ethylenic double bond, in the presence of a nickel catalyst and a triaryl phosphite. This reaction may be carried out in the presence or absence of a solvent.
When a solvent is used in this prior art process, it is preferably a hydrocarbon such as benzene or xylenes, or a nitrile such as acetonitrile.
The catalyst is an organonickel complex containing ligands such as phosphines, arsines, stilbenes, phosphites, arsenites or antimonites.
The presence of a promoter to activate the catalyst, such as a boron compound or a metal salt, generally a Lewis acid, is also described in this '761 patent.
In this particular process, the reaction medium is completely organic and a principal disadvantage thereof is the difficulty of separating, at the end of the reaction, the hydrocyanation products from the catalytic solution containing a plurality of constituents (nickel complex, triaryl phosphite, promoter), with a view, in particular, to recycling the catalyst solution to a fresh hydrocyanation reaction. Such a separation is difficult and imperfect, and a substantial loss of catalyst occurs. In addition, the catalyst is present in the products of hydrocyanation.
FR-A-2,338,253 describes the hydrocyanation of compounds having at least one site of ethylenic unsaturation in the presence of an aqueous solution of a compound of a transition metal, in particular nickel, palladium or iron, and a sulfonated phosphine.
This process permits good hydrocyanation, in particular of pentenenitriles, and an easy separation from the catalytic solution by simple decantation.
The results obtained during this latter hydrocyanation reaction are relatively good with various substrates and in particular with functional olefins such as pentenenitriles. Nonetheless, the percentage of linear dinitrile compound formed relative to the totality of the isomers obtained generally does not exceed 65% to 70%.
Furthermore, the catalyst rapidly becomes deactivated.